Fuse link



Dec. 21, 1937. E F BOOTHE 2,102,882

FUSE LINK Filed April l2, 1937 Patented Dec. 21, 1937 UNITED STATES PATENT OFFICE FUSE LINK Application April 12, 1937, Serial N0. 136,285

8 Claims.

This invention relates generally to fuse links, and more specifically to fuse links of the tension type provided with strain-absorbing means for relieving the fusible elements of the links of tensile strains which would be otherwise imposed thereon, the predominant object of the invention being to provide a fuse link with strain-relieving means of such construction and arrangement that, while the unruptured fuse link is provided 10 with great tensile strength quick separation of parts of the fuse link on rupture of the fusible element thereof is not unduly interfered with by the strain-absorbing means.

Fuse links of the type referred to above l5 ordinarily are adapted to be held under mechanical tension produced either by spring means which form parts of the fuse link structures, or parts of the protective apparatus with which the fuse links are associated, the purpose being to create a wide gap between the severed ends of the fusible element of a fuse link after same has become ruptured by passage of abnormal current, and to quickly extinguish any arc attending the blowing of the fusible element by causing the ruptured ends thereof to ily apart under the action of the spring tension.

A heretofore prevailing diillculty inherent in tension fuse links, particularly those of low or fractional ampere current carrying capacity, re-

sulted from the tendency of the fusible element to become severed by reason of the mechanical forces applied thereto, or if not actually severed the application of such forces to the fusible element for a long period of time resulted in alteration of the operating characteristics, or rating of the fuse link. In other words, it has been determined that an unstressed fuse wire which is intended to become ruptured upon passage therethrough of. say, three-fourths of an ampere,

when held under mechanical tension of the order produced by spring means found in the usual types of protective apparatus, is ruptured by currents of a magnitude substantially less than the figure specified.

The purpose of this invention, therefore, is to provide a fuse link construction which will not be harmfully affected by the application thereto of relatively high mechanical forces, by relieving 50 in an improved manner the fusible element of the improved fuse link structure of the forces produced by the tensioning means.

Fig. 1 is a longitudinal section of the improved fuse link.

5 Fig. 2 is a view similar to Fig. 1 but illustrating (Ci. 20u-117) theimproved fuse link when viewed from a din'erent angle.

Fig. 3 is an enlarged cross-section taken on line 3 3 of Fig. l.

Fig. 4 is an enlarged cross-section taken on 5 line 4-4 of Fig. l.

Fig. 5 is a fragmentary view illustrating a slightly modified form of the invention In the drawing, wherein is shown for the purpose of illustration, merely, two embodiments of 10 the invention, A designates the improved fuse link generally. The fuse link A includes a terminal i provided at its outer end with a contact head or cap 2. Secured to the inner end portion ofthe terminal I is an adapter 3 formed of 15 suitable electrical conducting material, said adapter being attached to said terminal i by a pin or other suitable securing element I which is driven into openings 5 formed in spaced portions of the adapter and through an opening S formed 26 through the terminal portion which is extended between said spaced adapter portions. The adapter 3 is provided with an opening 1 formed therein which is open at the lower end thereof as said adapter is illustrated in Figs. 1 and 2 and 25 the wall of this opening is screwthreaded throughout the greater part of the length of the opening.

Screwed into the' screwthreaded opening 1 formed in the adapter 3 is a terminal screw 8 30 formed of electrical conducting material, through which a centrally located opening 9 is formed from end to end thereof. The lower portion of the terminal screw has screwthreadedly connected thereto a sleeve I0 which is formed of suitable 35 electrical conducting material, said sleeve being internally screwthreaded for a considerable distance from its upper end as illustrated in Figs. 1 and 2 wherein the screwthreaded portion of the sleeve is designated by the reference character I0. When the sleeve I0 is screwthreadedly attached to the adapter through the instrumentality of the terminal screw 8 to provide the assembled fuse link the upper end of said sleeve, as illustrated in Figs. 1 and 2, abuts against the 45 lower end of the adapter 3.

Disposed within the sleeve i0 so that the lower end portion il thereof extends downwardly beyond the corresponding end of said sleeve is a tube Il formed of suitable insulating material. By preference I form this tube il of horn ber because this material is characterized by the ability to give oi! a gas when subjected to the heat of an electric arc which tends to extinguish the electric arc. In order to secure the tube Il in place within the sleeve i@ provide the upper end portion of the tube, as this element is illustrated in Figs. l and 2 ofthe drawing, with external screwthreads, and the screwthreads of the tube are screwed into engagement with the screwthreads of the sleeve i0.

At the end of the fuse link A opposite to the end at which the terminal l is located a exible energy-conducting cable i2 is provided. This cable has fixed to it a suitable solder lug i3 which is in tight frictional engagement with the cable and is soldered thereto. The upper end portion i3' of this solder lug, as this element is illustrated; in Figs. l and 2, is of reduced thickness and an aperture ld is formed through said portion of said solder lug which opening serves a purpose to be hereinafter set forth.

Extended transversely of the fuse link is a pin it which is formed of iiber or other suitable electrical insulating material, said pin being secured in place by having its opposite end portions disposed in opposed pairs of alined openings formed through the walls of the tube il and the sleeve l@ as is shown to the best advantage in Figs. 2 and 4. Arranged in embracing relation with the pin i5 is a strain wire lli which is formed so as to produce a loop as shown in Fig. 1 through which the pin l5 extends. The opposite end portion of the strain wire is shaped to provide a smaller loop a portion of which extends through the aperture lil formed through the portion it' of the solder lug I3, said smaller loop of the strain wire preferably being soldered to the solder lug HB, as indicated at ll in Fig. l, so as to provide good electrical connection between the parts.

The fusible element of the improved fuse link, which is designated by the reference character l@ in the drawing, is extended through the opening 9 formed in the terminal screw 8, and an end of said fusible element is soldered, as indicated at i9 in Figs. 1, 2 and 3 to the top face of the terminal screw. The fusible element extends downwardly from the terminal screw ii in a loose and untensioned manner and its lower end is soldered'to the portion of the loop of the strain wire i6 which extends about the pin l5. The sleeve i@ and the tube il have formed therethrough alined openings 26 and 2i. These openings are alined transversely of the fuse link with respect to the portion of the loop of the strain Wire ld that passes about the pin l5, and said openings perform an important function in the operation of the fuse link which will be hereinafter described.

Arranged in embracing relation with respect to the lower end portion of the tube i'i and contacting at its upper end with the end of the sleeve lil is a tube 22 formed of suitable insulating material. 4The tube 22 embraces the solder lug i3 and adjacent portions of the strain wire ld and the cable l2 and a tubular element 23 is extended upwardly into the lower end portion of said tube 22. The tubular element 23 is provided at its lower end with an outwardly extended annular ange 2d, and interposed under compression between this annular iiange and the lower end face of the tube 22 is a coilspring 25. The coilspring 25 tends to move the tubular element 23 downwardly but such downward movement of said tubular element is normally prevented by a member 26 which is secured to the cable l2 andy receives the-lower end of the tubular element 23 in engagement therewith.

in the use of the improved fuse link the norl groesse mal electrical circuit through said fuse link is from the terminal i, through the connection (the pin Il) to the adapter 3 and from said adapter to the terminal screw d. From the terminal screw the circuit leads through the soldered joint I9 to the fusible element IB and through said fusible element to the strain wire I6, the current passing through both legs of the strain wire to the solder lug i3 and then through the cable l2. It is of extreme importance to note that the strain wire i6 and the fusible element i8 are arranged in electrical series connection with each other and that said strain wire is a part of the normal electrical circuit through the fuse link.

When in the use of the improved fuse link passage of abnormal current through the fuse link occurs the fusible element is ruptured by such abnormal current. The electrical circuit through the fuse link then extends from the terminal i to the adapter 3 and from the adapter to -the sleeve lli. The current then jumps through the opening 2l formed in the wall of the tube Il, across the air gap between the Wall of the opening 20 in the sleeve iii and the strain wire it, the heat of the electric arc so formed being suflicient to break the strain wire and allow the severed ends of the ruptured fusible element to be quickly drawn apart by the coilspring 25.

lin the case of relatively small capacity fuses the fusible element iii is soldered to the strain wire as shown in Fig. l. For fuses of larger capacity where the normal current is too great to be carried by the strain wire above, the fusible element la may be extended, as shown in Fig. 5, on down along one leg of the strain wire 16a (the leg remote from the arcing holes 20 and 2l) to the solder lug I3a to which said fusible element is soldered. When the arrangement shown in Fig. 5 is employed the fusible elementlBa is soldered to the strain Wire Ita at the first point of contact between these elements, the point 2l in Fig. 5, so that the strain wire forms a fixed part of the normal electrical circuit through the fuse link.

I claim:

1. A. fuse link assembly including an energycarrying element, a fusible element electrically connected to said energy-carrying element, a second energy-carrying element, a strain wire electrically connected to said fusible element and electrically and mechanically connected to said r second energy-carrying element so as to be a fixed part of the normal electrical circuit through the fuse link assembly, an element forming a part of the fuse link assembly to which said strain wire is mechanically connected whereby said strain wire serves to relieve said fusible element of mechanical tensional strain, and an element formed of electrical conducting material spaced from a portion of said strain wire to provide a gap therebetween, said element being adapted on rupture of said fusible element to serve a conductcr for electrical energy whereby an electrical arc is produced across the gap between said element and said strain wire which severs said strain wire .and thereby allows the severed ends of the fusible element to be drawn apart.

2. A fuse link assembly including an energycarrying member, a fusible element electrically connected to said energy-carrying member, insulating means mechanically connected to said energy-carrying member, a second energy-carrying member, a strain wire electrically connected to said fusible element and to said second energycarrying member so as to be a fixed part of the normal electrical circuit through the fuse link assembly, means for mechanically connecting said strain wire to said insulating means so as to relieve said fusible element of mechanical tensional strain, and an element formed of electrical conducting material electrically connected to the first-mentioned energy carrying member and spaced from a portion of said strain wire to produce a gap therebetween, said element being adapted on rupture of the fusible element to serve as a conductor for electrical energy whereby an electrical arc is produced across the gap between said element and said strain wire which severs said strain wire and thereby allows the severed ends of the fusible element to be drawn apart.

3. A fuse link assembly including an energycarrying member, a fusible element electrically connected to said energy-carrying member, tubular insulating means mechanically connected to said energy-carrying member, a second energycarrying member, a strain1 wire electrically connected to said fusible element and to said second energy-carrying member so as to be a fixed part of the normal electrical circuit through the fuse link assembly, means for mechanically connecting said strain wire to said tubular insulating means so as to relieve said fusible element of mechanical tensional strainand a tubular element formed of electrical conducting material electrically connected to the first-mentioned energycarrying member and spaced from a portion of said strain wire to produce a gap therebetween, said tubular element being adapted on rupture of the fusible element to serve as a conductor for electrical energy whereby an electrical arc is produced across the gap between said tubular element and said strain wire which severs said strain Wire and thereby allows the severed ends of the fusible element to be drawn apart.

4. A fuse link assembly including an energycarrying member, a fusible element electrically connected to said energy-carrying member, tubular insulating means mechanically connected to said energy-carrying member, a second energycarrying member, a strain wire electrically connected to said fusible element and to said second energy-carrying member so as to be a xed part of the normal electrical circuit through the fuse link assembly, means for mechanically connecting said strain wire to said tubular insulating means so as to relieve said fusible element of mechanical tensional strain, and a tubular element formed of electrical conducting material embracing said tubular insulating means, said tubular element being electrically connected to the firstmentioned energy-carrying member and spaced from a portion of said strain wire to produce a gap therebetween, said tubular element being adapted on rupture of the fusible element to serve as a conductor for electrical energy whereby an electrical arc is produced across the gap between said tubular element and said strain wire which severs said strain wire and thereby allows the severed ends of the fusible element to be drawn apart.

5. A fuse link assembly including an energycarrying member, a fusible element electrically connected to said energy-carrying member, tubular insulating means mechanically connected to said energy-carrying member, a second energy-carrying member, a strain wire electrically connected to said fusible element and to said second energy-carrying member so as to be a fixed part of the normal electrical circuit through the fuse link assembly, means for mechanically connecting said strain wire to said tubular insulating means so as to relieve said fusible element of mechanicall tensional strain, and a tubular element formed of electrical conducting material electrically connected to the first-mentioned energy-carrying member and embracing said tubular insulating means, said tubular insulating 'means having an opening formed in the wall thereof which provides a gap between said tubular element and a portion of said strain wire, said tubular element being adapted on rupture of said fusible element to serve as a conductor for electrical energy whereby an electrical arc is produced which passes through the opening formed in said insulating means from the tubular element to the strain wire whereby said strain wire is severed by said electrical arc so as to allow the severed ends of the fusible element to be drawn apart.

6. A fuse link assembly including an energycarrying member, a fusible element electrically connected to said energy-carrying member, tubular insulating means mechanically connected to said energy-carrying member, a second energy-carrying member, a strain wire electrically connected to said fusible element and to said second energy-carryingmember so as to be a fixed part of the normal electrical circuit through the fuse link assembly, means for mechanically connecting said strain wire to said tubular insulating means so as to relieve said fusible element of mechanical tensional strain, and a tubular element formed of electrical conducting material electrically connected to the first-mentioned energy-carrying member and embracing said tubular insulating means, said tubular insulating means and said tubular element having alined openings formed in the walls thereof, said tubular element being adapted on rupture of said fusible element to serve as a conductor for electrical energy whereby an electrical arc is produced which passes through the opening formed in said insulating means from the wall of the opening in said tubular element to the strain wire whereby said strain wire is severed by said electrical arc so as to allow the severed ends of the fusible element to be drawn apart.

7. A fuse link assembly including an energycarrying member, a fusible element electrically connected to said energy-carrying member, tubular insulating means mechanically connected to said energy-carrying member, a second energy-carrying member, a strain wire electrically connected to said fusible element and to said second energy-carrying member so as to be a fixed part of the normal electrical circuit through the fuse link assembly, means comprising a transversely extended pin for mechanically connecting said strain wire to said tubular insulating means so as to relieve said fusible element of mechanical tensional strain, and a tubular element formed of electrical conducting material electrically connected to the first-mentioned energy-carrying member and embracing said tubular insulating means, said tubular insulating means and said tubular element having alined openings formed in the walls thereof, said tubular element being adapted on rupture of said fusible element to serve as a conductor for electrical energy whereby an electrical arc is produced which passes through the opening formed in said insulating means from the wall of the opening in said tubular element to the strain wire whereby said strain wire is severed by said electrical are so as to allow the severed ends of of the fusible element to be drawn apart.

8. A fuse link assembly including an energycarrying member, a fusible element electrically connected to said energy-carryingmember, tubular insulating means mechanically connected to said energy-carrying member', a second energy-carrying member, a strain wire electrically connected to said fusible element and to said second energy-carrying member so as to be a xed part of the normal electrical circuit through the fuse link assembly, means comprising a transversely extended pin formed of insulating material for mechanically connecting said strain wire to said tubular insulating means so as to relieve said fusible element of mechanical tensional strain, and a tubular element formed of electrical conducting material electrical1y1con= nected tol the rst-mentioned energy-carrying member and embracing said tubular insulating means, said tubular insulating means and said tubular element having alined openings formed in the Walls thereof, said tubular element being 

